The term "electroerosion" is used herein to refers to a machining process in which electric energy is supplied across a machining gap formed between a tool electrode and a conductive workpiece and flushed with a machining fluid to remove material from the workpiece by the action of successive time-spaced electrical discharges effected across the gap (electrical discharge maching or EDM), the action of electrochemical or electrolytic solubilization (electrochemical machining or ECM) or a combination of these actions (electrochemical-discharge machining or ECDM). In EDM, the machining fluid is commonly a liquid which is basically electrically nonconductive or of dielectric nature and typically constituted by deionized water, a liquid hydrocarbon or a combination of such water and hydrocarbon. The electric energy is supplied commonly in the form of a succession of voltage pulses which result in a corresponding succession of pulsed, discrete electrical discharges across the machining gap. In ECM, the machining fluid is commonly a liquid electrolyte which is naturally conductive, and the machining current may be a direct current but is preferably in the form of pulses or pulsating current. In ECDM, the machining fluid is typically a liquid having both dielectric and electrolytic natures and may be tap water or water deionized to retain weak conductivity.
In traveling-electrode (TE) electroerosion, the tool electrode is constituted by a continuous electrode element which is typically a conductive wire having a diameter ranging from 0.05 mm to 0.5 mm, but may take the form of a tape or ribbon of similar thickness. Such electrode is broadly and generally referred to herein as a continuous electroeroding electrode. The electrode is axially transported continuously from a supply reel to a takeup reel through a machining zone in which a workpiece is disposed. The machining zone is commonly defined by a pair of machining guide members which support the traveling electrode and establish a straight-line electrode path across the workpiece. Electrode traction and braking units allow the continuous electrode to be tightly stretched and kept taut between the supply and the takeup and to be axially driven between the machining guide members while traversing the workpiece from one side thereof to the other side thereof along the straight-line path, thus presenting the continuously renewed electrode surface juxtaposed in an electroerosive cutting relationship with the workpiece across a narrow machining gap. The machining gap is flushed with a machining liquid medium and electrically energized with a high-density electrical machining current which is passed between the electrode and the workpiece to electroerosively remove material from the latter. The roles of the machining liquid medium in the electroerosive process are to carry the erosive machining current, to carry away the machining chips and other gap products, and to cool the traveling, thin continuous electrode and the workpiece.
In the conventional TE-electroerosion machine design, the electrode supply and takeup reels are mounted on the machine frame and so are the traction and braking units constituting an electrode feed means and are also the electrode guide members. The machine frame commonly includes a pair of arms having their ends between which the workpiece is disposed. These end portions are arranged to support the guide members which define thereacross the afore-mentioned straight-line electrode path traversing the workpiece. The traction and braking units and the supply and takeup reels are securely mounted on these arms and/or a base portion from which they extend in the machine frame which is, of course, secured in position. The workpiece is securely mounted on a worktable of compound cross-feed configuation which is displaced in a horizontal plane relative to the straight-line path transversely to advance electroerosion in the workpiece along a programmed machining path.
With the machine design described, it has been found that problems arise where a massive workpiece is to be machined. Thus, not only must the compound worktable have strokes of displacement which are unpractically long to cover a large displacement area, but the erosive machining action tends to become unstable or inaccurate. As the workpiece thickness is increased, there results a corresponding increase in the machining pressure which tends to deflect the traveling electrode backwards along the machining path, thus causing it to deviate from the established straight-line guide path. The increasing machining pressure can be countered by increasing the tension or the forward and/or backward tractions applied through the electrode feed means to the traveling electrode. It has been found, however, that this also brings about an increase in the unfavorable load on the arms supporting the guide means to the extent that the arms deflect to cause a serious guide-positioning and hence machining error.